Integrated circuits such as computer chips are manufactured from silicon wafers. The silicon wafers need to be maintained in extremely clean and contamination free environments during their transport and in between manufacturing process steps. Additional, required or desirable characteristics of containers to transport and/or store semiconductor wafers include light weight, rigidity, cleanliness, limited gaseous emissions, and cost effective manufacturability. The containers provide hermetic or close to hermetic isolation of wafers when the containers are closed. Simply stated, such containers need to keep the wafers clean, uncontaminated, and undamaged.
Plastic containers have been used for decades for transporting and storing wafers in-between process steps. Selected polymer materials provide adequate characteristics. Such containers have highly controlled tolerances for interfacing with processing equipment as well as the equipment/robots that transport the containers. Moreover, it is desirable in such plastic containers to utilize components that are attachable and removable without using metallic fasteners such as screws. Metal fasteners cause particle generation when inserted and removed.
Driven by cost efficiencies and improved manufacturing capabilities, the size of wafers utilized in manufacturing semiconductors has been increasing. Now several fabrication facilities utilize 300 mm wafers. As the size of wafers has increased and the density of the circuits has increased making the circuits susceptible to smaller and smaller particles and other contaminants. Thus, as the wafers have increased in size, the containers have increased in size as well; the requirements of keeping the wafers clean and contaminant free have become more stringent due to the wafers being more susceptible to smaller particles and other contaminants, containers have increased in size. Additionally, carriers need to maintain their capabilities under the rigors of robotic handling which includes lifting the carrier by the robotic flange positioned at the top of the container.
Front opening wafer containers have become the industry standard for transporting and storing large diameter 300 mm wafers.
In such wafer containers the front door is latchable to a container portion and closes a front access opening through which the wafers are robotically inserted and removed. When the container is fully loaded with wafers the door is inserted into the door frame of the container portion and latched thereto. When seated the cushions on the door then provide upward, downward, and inward constraint.
A problem discovered in fabricating front opening plastic containers for holding and/or transporting larger wafers, for example 300 mm containers, is that the expanses of plastic utilized on the top, bottom, sides, front, and back of the container may flex due to the increased weight of the wafer load. Particularly, when the container is picked up by the robotic flange affixed to the top of the container. The flexing can compromise the sealing of the door to door frame by distorting the shape of the door frame, essentially elongating it in the vertical direction. Also, the flexing can affect the container to wafer engagement, more particularly, the constraints that the wafer supports provide to the wafers is altered.
It is conventional wisdom in 300 mm wafer containers to avoid using metal in any fashion. Interlocking flanges with are used for attachment of accessories such as robotic flanges and side handles. Plastic leaf springs that are part of the engaging components and that form detents are utilized to retain the components, such as robotic flanges in place. See U.S. Pat. No. 6,010,008, owned by the owner of this application, and incorporated herein by reference. Such robotic flanges extend in the z direction utilizing flanges extending also in the z direction. The detents operate only to maintain the cooperating structures and stay properly positioned on the flanges without carrying any appreciable loading through the detent structures, for example the resiliently bendable portion of such detents extend in the z direction and bend about an axis in the x direction. Thus, the direct loading on the robotic flange to container portion connection is primarily in the y direction and is carried through the horizontally extending flanges. When such containers are fully loaded and robotically supported by the robotic flange, stress analysis studies confirms that the primary stresses are found on the top and sides adjacent the flanges as opposed to the back side and front side. From a structural perspective, it would be preferable to better distribute the load carrying forces more uniformly on the back of the carrier portion to minimize deflection issues.
This problem has been addressed to some extent by utilizing robotic flanges that effectively saddle the container portion and extend down the sides of the containers such that the load of the wafers is not transferred totally through the side walls of the carrier, see U.S. Pat. No. 7,347,329 assigned to the owner of the instant application and incorporated herein by reference.
The semiconductor industry is now moving toward utilizing larger, 450 mm diameter wafers. The larger diameter wafers, although providing cost efficiencies, also provide increased fragility, greater weight, and present undiscovered issues associated with handling and storing the larger wafers in containers made of plastic. The flexing and corresponding problems associated with the expanses of plastic on the top, bottom, sides, front, and back are exacerbated.
With the significant leaps in the size of processed wafers, new issues and problems arise that were not present with smaller sized wafers. Many standards for 450 mm wafers, such as the number of wafers in containers and the spacing between wafers, may very well remain the same as 300 mm wafer container standards due to existing equipment compatibilities and cost pressures. And, of course, as wafers get larger in diameter, they correspondingly get heavier. A wafer container that holds the same number of 450 mm wafers as is provided in standardized 300 mm containers is expected to weigh approximately 40 pounds. At this weight, manual handling starts to become more difficult.
Using comparable thicknesses of polymer walls for a larger container may not provide sufficient structural rigidity of the container. That is, the container would be expected to be less dimensionally stable under loading, transfer and shipping due to the greater dimensions and greater expanses of polymer. Thickening the walls and adding significant strengthening structure would further increase the weight of 450 mm wafer containers.
Moreover, conventional 300 mm wafer containers are typically injection molded. It is anticipated that it will be difficult to adequately control the dimensions of larger containers utilizing comparable injection molding practices and comparable or larger wall thicknesses. Currently 300 mm wafer containers generally utilize the shell as the principal structural member for positioning components that interface with wafers and outside equipment, namely the wafer supports and the kinematic coupling machine interface.
In addition, the open interior volume will significantly increase as will the area of the open front that sealingly receives the door. This suggests more difficult sealing issues between the door and the container portion.
Wafers of larger dimensions will also have significantly greater sag which will make them more susceptible to damage during handling and transport and require unique support not required for smaller wafers. This greater sag presents challenges in maintaining the desired spacing between wafers while still allowing placement and removal of the wafers robotically by robotic arms.
Accordingly, it would be desirable to develop front opening configurations for 450 mm wafer containers that have design attributes for minimizing wafer sag and minimizing weight of the container. In addition, configurations providing improved sealing characteristics for the doors would be desirable. Moreover, configurations providing enhanced wafer support to accommodate storing of 450 mm wafers in wafer containers as well during robotic handling of the wafers would be desirable.